1. Field of the Invention
This invention relates to power factor correction (PFC) front-end rectifier, and more particularly to a PFC rectifier that has independently coupled inductive components.
2. Description of the Prior Art
Electromagnetic devices have been used in a wide variety of power supply applications. These devices generally comprise a magnetic core and one or more windings. Some power supplies use multiple electromagnetic devices at various stages of their power conversion circuitry. Conventionally, magnetic cores of the multiple electromagnetic devices has been integrated to increase the power density and decrease the component count of power supplies.
Known power conversion circuitry have used an integrated magnetic core to achieve magnetic coupling between two filter inductors. An integrated magnetic core is also used for magnetically coupling a filter inductor and a resonant inductor. In these known approaches, however, the voltage waveforms across the magnetically coupled inductors are proportional to each other.
In some applications, it is desired that the voltage waveforms across the windings not to be proportional. FIG. 1 shows a known multi-port electromagnetic device that couples two windings in this manner. However, under this arrangement, one winding of the multi-port electromagnetic device of FIG. 1 is significantly influenced by the applied voltage across the other winding. In other words, the two windings of the multi-port electromagnetic device of FIG. 1 are dependent on each other because of their mutual inductance.
In some applications, it is necessary to provide a multi-port electromagnetic device having independent windings. For example, in power supplies that have multiple converter stages, the inductive components in one stage should be independent of each other. This requirement makes the multi-port electromagnetic device of FIG. 1 unsuitable because of its dependent inductive components.
One known approach that provides independent inductive components uses an orthogonal magnetic flux, whereby an induced magnetic flux in one winding is perpendicular to the magnetic flux induced in another winding. As a result, the two windings could be wound on the same magnetic core, while behaving as independent inductors. However, the structure of the windings on the magnetic core for creating orthogonal magnetic flux is too complex.
FIG. 2 shown another known multi-port electromagnetic device that uses a pair of E-shaped magnetic cores with symmetrical and asymmetrical windings to provide independent inductive components. However, in the multi-port electromagnetic device of FIG. 2, the reluctances of the two outer legs of the E core must be identical, otherwise the magnetic flux generated by the winding on the middle leg is not equally distributed to the outer legs. As a result, the induced voltage across the windings of the outer legs are significantly influenced by the voltage across the winding on the inner leg, which causes the two windings not to be magnetically independent of each other.
In a co-pending patent application Ser. No. 11/062,446, which is assigned to the assignee of the present invention and is hereby incorporated by reference in its entirety, the inventors of the instant application disclosed an “Electromagnetic Device Having Independent Inductive Components.” The disclosed electromagnetic device includes two groups of windings, with each group of windings storing decoupled magnetic energy in commonly used magnetic cores, i.e., the two groups of windings are magnetically independent. Each group of windings consists of at least one winding. For example, to obtain two independent inductors, a single winding from each group is required, as further described below.
PFC rectifiers in the front-end of a power supply draw an ac input current from an ac input voltage source to meet harmonic standards for power supplies by reducing harmonic contents of input current waveforms. PFC front-end rectifiers in general employ one or more boost converters, which have corresponding inductive components. One conventionally employed technique for correcting power factor uses a front-end full bridge rectifier followed by a boost converter. Also known is a PFC rectifier that eliminates two of the four input bridge diodes located in the series power path of the PFC rectifier. FIG. 3 shows one such PFC rectifier, which uses two boost converters to achieve high power factor with two input diodes. Each boost converter is connected to the ac input source in opposite polarity and operates during one half line cycle of the ac input voltage. As shown in FIG. 3, a first boost converter is connected to a first terminal of the ac input voltage source and a second boost converter is connected to a second terminal of the ac input voltage source. Each boost converter operates during one half line cycle of the ac input voltage. As shown in FIGS. 4 and 5, one boost converter operates while the other boost converter is idle (shown in dotted lines). As a result, the utilization of switches and inductive components is only one half of the conventional PFC boost converter that always utilizes all the components during the entire line cycle. The low utilization of the inductive components may be a serious penalty in terms of size, weight and power density of the power supply.
Therefore, there exists a need for a PFC rectifier that utilizes its inductive components more efficiently to overcomes the above mentioned drawbacks.